Small Solar-System Bodies l Small Bodies News Small Solar-System Bodies The title The Nine Planets is somewhat misleading. In addition to the (eight) planets and their satellites the solar system contains a large number of smaller but interesting objects. Small Bodies There are thousands of known asteroids and comets and undoubtedly many more unknown ones. Most asteroids orbit between Mars and Jupiter . A few (e.g. 2060 Chiron) are farther out. There are also some asteroids whose orbits carry them closer to the Sun than the Earth (Aten, Icarus, Hephaistos). Most comets have highly elliptical orbits which spend most of their time in the outer reaches of the solar system with only brief passages close to the Sun. And there is a large and important class of Trans-Neptunian Objects or Kuiper Belt Objects (including Pluto) that orbit (mostly) beyond Neptune. The distinction between comets and asteroids is somewhat controversial . The main distinction seems to be that comets have more volatiles and more elliptical orbits.

But there are interesting ambiguous cases such as 2060 Chiron (aka 95 P/Chiron) and 3200 Phaethon which seem to share some aspects of both categories. Asteroids are sometimes also referred to as minor planets or planetoids (not to be confused with "lesser planets" which refers to Mercury and Pluto ). Some of the largest asteroids and Kuiper Belt objects may be classified as dwarf planets. Very small rocks orbiting the Sun are sometimes called meteoroids to distinguish them from the larger asteroids. When such a body enters the Earth's atmosphere it is heated to incandescence and the visible streak in the sky is known as a meteor. If a piece of it survives to reach the Earth's surface it is known as a meteorite. Millions of meteors bright enough to see strike the Earth every day (amounting to hundreds of tons of material). All but a tiny fraction burn up in the atmosphere before reaching the ground. The few that don't are our major source of physical information about the rest of the solar system. Finally, the space between the planets is not empty at all. It contains a great deal of microscopic dust and gas as well as radiation and magnetic fields.

Kuiper Belt Objects: Facts about the Kuiper Belt & KBOs Kuiper Belt Objects: Facts about the Kuiper Belt & KBOs By Nola Taylor Redd, Space.com Contributor | January 22, 2016 01:06pm ET MORE This artist's impression shows the distant dwarf planet Eris in the distance with its moon Dysmonia in the foreground. New observations have shown that Eris is smaller than previously thought and almost exactly the same size as Pluto. Eris is extremely reflective and its surface is probably covered in frost formed from the frozen remains of its atmosphere. Dysnomia appears to be a darker and less reflective body. Credit: ESO/L. Calçada Beyond the gas giant Neptune lies a region of space filled with icy bodies. Known as the Kuiper Belt, this chilly expanse holds trillions of objects, remnants of the early solar system. Dutch astronomer Jan Oort first proposed in 1950 that some comets might come from the the solar system’s far suburbs. That reservoir later became known as the Oort cloud.

Earlier, in 1943, astronomer Kenneth Edgeworth had suggested comets and larger bodies might exist beyond Neptune. In 1951, astronomer Gerard Kuiper predicted the existence of a belt of icy objects that now bears his name. Some astronomers refer to it as the Edgeworth-Kuiper Belt. Astronomers are now hunting for a planet in the Kuiper Belt, a true ninth planet , after evidence of its existence was unveiled on Jan. 20, 2016. The so-called "Planet Nine," as scientists are calling it, is about 10 times the mass of Earth and 5,000 times the mass of Pluto. Let's take a closer look at this distant section of the solar system and the small worlds most commonly known as Kupier Belt Objects (KBOs) and, in recent years, dwarf planets. Artists rendering of the Kuiper Belt and Oort Cloud. Credit: NASA Artist's concept of the dwarf planet Haumea and its two satellites (Hi’iaka and Namaka).

Credit: SINC/José Antonio Peñas The Kuiper Belt is an elliptical plane in space spanning from 30 to 50 times Earth's distance from the sun, or 2.5 to 4.5 billion miles (4.5 to 7.4 billion kilometers). The belt is similar to the asteroid belt found between Mars and Jupiter, although the objects in the Kuiper Belt tend more to be icy rather than rocky. Scientists estimate that thousands of bodies more than 62 miles (100 km) in diameter travel around the sun within this belt, along with trillions of smaller objects, many of which are short-period comets . The region also contains several dwarf planets , round worlds too large to be considered asteroids and yet not qualifying as planets because they’re too small, on an odd orbit, and don’t clear out the space around them the way the 8 planets do. Kuiper Belt formation When the solar system formed , much of the gas, dust and rocks pulled together to form the sun and planets. The planets then swept most of the remaining debris into the sun or out of the solar system.

But bodies farther out remained safe from gravitational tugs of planets like Jupiter , and so managed to stay safe as they slowly orbited the sun. The Kuiper Belt and its compatriot, the more distant and spherical Oort Cloud , contain the leftover remnants from the beginning of the solar system and can provide valuable insights into its birth. The classical Kuiper Belt — the most crowded section — lies between 42 and 48 times Earth's distance from the sun. The orbit of objects in this region remain stable for the most part, although some objects occasionally have their course changed slightly when they drift too close to Neptune. Kuiper Belt Objects This artist's impression shows the distant dwarf planet Eris. New observations have shown that Eris is smaller than previously thought and almost exactly the same size as Pluto. Eris is extremely reflective and its surface is probably covered in frost formed from the frozen remains of its atmosphere. The distant Sun appears to the upper right and both Eris and its moon Dysnomia (center) appear as crescents. Credit: ESO/L. Calçada Pluto was the first true Kuiper Belt Object to be seen, although scientists at the time didn't recognize it as such.

The existence of the belt wasn't realized until scientists discovered a slow moving, small world in the outer solar system in 1992 (David Jewitt and Jane Luu found the KBO, 1992QB1.). Other objects soon followed, and astronomers quickly saw that the region beyond Neptune teemed with icy rocks and tiny worlds. Sedna (sed’nah), about three-fourths the size of Pluto, was discovered in 2004. It is so far out from the sun it takes about 10,500 years to make a single orbit. Sedna is about 1,100 miles (1,770 km) wide and circles the sun on an eccentric orbit that ranges between 8 billion miles (12.9 billion km) and 84 billion miles (135 billion km). In July 2005, astronomers announced the discovery of an object in the Kuiper Belt thought to be larger than Pluto, though subsequent observations revealed it was slightly smaller. Known as Eris , it orbits the sun approximately once every 580 years, traveling almost one hundred times farther from the sun than Earth does.

Eris' discovery revealed to some astronomers the problem of terming Pluto a full-scale planet, and in 2006, Pluto, Eris, and the largest asteroid Ceres were reclassified as dwarf planets. Two more dwarf planets, Haumea and Makemake , were discovered in the Kuiper Belt in 2008. Planet Nine Planet Nine orbits the sun at a distance that is 20 times farther out than the orbit of Neptune. (The orbit of Neptune is 2.7 billion miles from the sun at its closest point.) The strange world's orbit is about 600 times farther from the sun than the Earth's orbit is from the star. [ 'Planet Nine': Facts About the Mysterious Solar System World (Infographic) ] Scientists Mike Brown and Konstantin Batygin at the California Institute of Technology in Pasadena described the evidence for Planet Nine in a study published in the Astronomical Journal. The research is based on mathematical models and computer simulations using observations of six other smaller Kuiper Belt Objects with orbits that aligned in a similar matter. Exploration Because of their small size and distant location, Kuiper Belt Objects are a challenge to spot from Earth.

Infrared measurements from NASA's space-based telescope, Spitzer, have helped to nail down sizes for the largest objects. In order to catch a better glimpse of these remote leftovers from the birth of the solar system, NASA launched the New Horizons mission . The spacecraft reached Pluto in 2015 and continued on with an aim to examine multiple KBOs. HubbleSite - Reference Desk - FAQs Reference Desk Frequently Asked Questions What is the solar system? The solar system consists of a central star, the Sun, and all of the smaller celestial bodies that continuously travel around it. The smaller bodies include eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune, which are themselves orbited by more than 140 moons. (Only Mercury and Venus have no moons.) In addition, the solar system contains millions of rocky asteroids and billions of icy comets. All of these objects are held together in a group by the Sun's gravity. How did the solar system form? The planets, asteroids and comets in the solar system are loose objects left over from the formation of the Sun.

Originally the gas and dust that would become the Sun was the core of a cloud much larger than the solar system, probably several light-years across. (One light-year is equal to approximately 6,000,000,000,000 miles.) The core was slowly rotating at first, but as it collapsed it spun faster, like a spinning ice-skater pulling in his arms. The rotation prevented the material at the core's equator from collapsing as fast as material at the poles, so the core became a spinning disk. Gas and dust in the disc spiraled gradually in to the center, where it accumulated to form the Sun. But because dust is denser than gas, some of the dust settled to the mid-plane of the disc. These dust particles stuck together to make clumps, then clumps stuck together to make rocks, then rocks collided to make planets. In the case of the "gas giant" planets, Jupiter, Saturn, Uranus and Neptune, the rocky cores were massive enough to also attract some of the gas. The outer layers of these planets are made up of hydrogen and other gases.

So the Sun is the collapsed core of an interstellar gas cloud, and the planets, asteroids and comets are small lumps of dust or ice chunks which stayed in orbit instead of spiraling into the Sun. The planets all formed within a very short period, probably a few million years, about five billion years ago. How old is the solar system? The solar system is about 4.6 billion years old. How big is the solar system? There are no physical boundaries in space. The solar system consists of eight planets orbiting around one star: the Sun. Neptune, the farthest planet from the Sun, orbits approximately 30astronomical units from the Sun. An astronomical unit is a unit of length used by astronomers. One astronomical unit equals the distance from Earth to the Sun: 93 million miles (149 million km). Some of the comets associated with the solar system travel on orbits that take them much farther from the Sun than Neptune. How many planets are there in our solar system? Our solar system officially has eight planets and one star: the Sun. In order from the Sun out, the planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

The discovery of an object larger than Pluto in 2005 rekindled the debate over whether such objects, belonging to the "Kuiper Belt" – a collection of icy bodies located beyond Neptune – should be called planets. Pluto and other large members of the Kuiper Belt are now considered "dwarf planets." Can you see any planets with the "naked eye?" Mercury, Venus, Mars, Jupiter and Saturn can be seen with the unaided eye. That is how they were discovered by ancient civilizations. Uranus and Neptune were discovered using telescopes. Are there differences among the planets in our solar system? Planets come in different sizes, compositions and colors. The four planets closer to the Sun are called "rocky" planets. They are small in size and similar to Earth in composition. They have no rings and only two of them (Earth and Mars) have moons. The four outer planets, also called "gas giants," are much larger than the rocky planets. They all have rings and have many moons. The gas giants are made up mostly of hydrogen, helium, frozen water, ammonia, methane and carbon monoxide. Which planets are called the "rocky" or "terrestrial" planets?

Mercury, Venus, Earth and Mars are called "rocky" or "terrestrial" planets. They are similar to Earth in composition. Heat from the Sun evaporated lightweight elements like hydrogen and helium into interplanetary space. Mostly rock and metal was left in this zone and clumped together to form the inner rocky planets. Which planets are called the "gaseous" planets? Jupiter, Saturn, Uranus and Neptune are called the "gaseous" planets. Jupiter and Saturn contain the largest percentages of hydrogen and helium, while Uranus and Neptune contain the largest shares of ices – frozen water, ammonia, methane and carbon monoxide. Which planets have rings? The four gas giants, Jupiter, Saturn, Uranus and Neptune, have rings. How thick are Saturn's rings? The Hubble telescope has captured snapshots of Saturn with its rings nearly edge-on to our view. Read more about it . Saturn's rings are incredibly thin. The main rings are generally only about 30 feet (10 meters) thick, though parts of the main and other rings can be several kilometers thick.

The rings are made of dusty ice, in the form of boulder-sized and smaller chunks that gently collide with each other as they orbit around Saturn. Saturn's gravitational field constantly disrupts these ice chunks, keeping them spread out and preventing them from combining to form a moon. The rings have a slight pale reddish color due to the presence of organic material mixed with the water ice. Find out more from HubbleSite: Hubble discoveries about Saturn in NewsCenter . How close do Earth and Mars get? Mars and Earth are like two cars on a racetrack as they journey around the Sun. Earth is on the inside track and travels faster than Mars, which is on the outside. When Earth laps Mars about every two years, it comes as close as 35 million miles (56 million km) or as far away as 63 million miles (101 million km) because of Mars’ highly elongated orbit. What is a comet? Comets are small, fragile, irregularly shaped bodies composed mostly of a mixture of water ice (ice composed of H20), dust, and carbon- and silicon-based compounds. They have highly elliptical orbits that repeatedly bring them very close to the Sun and then swing them into space.

Comets have three distinct parts: a nucleus, a coma and a tail. The solid core is called the nucleus, which develops a coma with one or more tails when a comet sweeps close to the Sun. The coma is the dusty, fuzzy cloud around the nucleus of a comet, and the tail extends from the comet and points away from the Sun. The coma and tails of a comet appear only when the comet is near the Sun. Find out more from HubbleSite: Hubble discoveries about comets from NewsCenter . How did comets form? Comets are some of the material left over from the formation of the planets. Our entire solar system, including comets, was created by the collapse of a giant, diffuse cloud of gas and dust about 4.6 billion years ago. Much of the matter merged into planets, but some remained to form small lumps of frozen gas and dust in the outer region of the solar system, where temperatures were cold enough to produce ice. Find out more from HubbleSite: Hubble discoveries about comets from NewsCenter . Why do comets have tails? Comets are lumps of frozen water ice, gas and dust. As a comet approaches the Sun, it starts to heat up.

The ice transforms directly from a solid to a vapor, releasing the dust particles embedded inside. Sunlight and the stream of charged particles flowing from the Sun – the solar wind – sweeps the evaporated material and dust back in a long tail. The comet's ingredients determine the types and number of tails. What are the types of comet tails? There are two types of comet tails: dust and gas ion. A dust tail contains small, solid particles that are about the same size found in cigarette smoke. This tail forms because sunlight pushes on these small particles, gently shoving them away from the comet’s nucleus. Because the pressure from sunlight is relatively weak, the dust particles end up forming a diffuse, curved tail. A gas ion tail forms when ultraviolet sunlight rips one or more electrons from gas atoms in the coma, making them into ions (a process called ionization). The solar wind then carries these ions straight outward away from the Sun. The resulting tail is straighter and narrower. Both types of tails may extend millions of kilometers into space. As a comet heads away from the Sun, its tail dissipates, its coma disappears, and the matter contained in its nucleus freezes into a rock-like material. Where do comets come from?

Comets are found in two main regions of the solar system: the Kuiper Belt and the Oort Cloud. There are two types of comets: short-period comets and long-period comets. Short-period comets – comets that frequently return to the inner solar system – probably come from the Kuiper Belt beyond the orbit of Neptune. Astronomers estimate that this belt contains at least 200 million objects, which are thought to have remained essentially unchanged since the birth of the solar system 4.6 billion years ago. Long-period comets, which can take thousands of years to complete their orbits, are thought to emanate from the Oort Cloud, a vast group of frozen bodies in the outer part of the solar system. The Oort Cloud is thought to extend 50,000 times the distance from the Earth to the Sun. Oort Cloud comets, like their Kuiper Belt brothers, probably originated in the region of the solar system between Jupiter and Neptune, but were ejected from to the Oort Cloud by close encounters with the gravity of the giant planets.

Comets are kicked out of the Oort Cloud and the Kuiper Belt by the pull of the gravity of another object – a planet, a star, or another small body. They then begin their journey toward the inner solar system and the Sun. What path do comets follow through the solar system? Planets have nearly circular orbits, but comets have elongated paths around the Sun. A comet is at "aphelion" when its orbit is farthest from the Sun. It is at "perihelion" when it is closest to the Sun. Due to angular momentum, a comet will travel fastest at perihelion and will slow down as it approaches aphelion. Comets can be classified by their orbital period: that is, the time it takes them to make one complete trip around the Sun. Comets with short and intermediate orbital periods of less than 200 years – like Comet Halley, whose orbital period is 76 years – spend most of their time between Pluto and the Sun. These comets originally formed in the Kuiper Belt, but a gravitational "push" from the planets, especially Jupiter, swung them closer to the Sun.

A long-period comet will have an orbital period of more than 200 years. Comet Hale-Bopp, for example, completes an orbit about every 4,000 years. Scientists think that this type of comet spends most of its time way out in the Oort Cloud at the farthest edge of our solar system. What is the difference between a meteor, a meteoroid, a meteorite, an asteroid and a comet? Most of us probably have seen meteors or shooting stars. A meteor is the flash of light that we see in the night sky when a small chunk of interplanetary debris burns up as it passes through our atmosphere. "Meteor" refers to the flash of light caused by the debris, not the debris itself. The debris is called a meteoroid. A meteoroid is a piece of interplanetary matter that is smaller than a kilometer and frequently only millimeters in size. Most meteoroids that enter the Earth's atmosphere are so small that they vaporize completely and never reach the planet's surface. If any part of a meteoroid survives the fall through the atmosphere and lands on Earth, it is called a meteorite.

Although the vast majority of meteorites are very small, their size can range from about a fraction of a gram (the size of a pebble) to 100 kilograms (220 lbs) or more (the size of a huge, life-destroying boulder). Asteroids are generally larger chunks of rock that come from the asteroid belt located between the orbits of Mars and Jupiter. Comets are asteroid-like objects covered with ice, methane, ammonia, and other compounds that develop a fuzzy, cloud-like shell called a coma and sometimes a visible tail whenever they orbit close to the Sun. Find out more from HubbleSite: Hubble discoveries about asteroids , comets , and Kuiper Belt objects from NewsCenter . What is the asteroid belt? The asteroid belt is a zone between the orbits of Mars and Jupiter. Scientists believe that the asteroids in the asteroid belt never formed a planet because the gravity of nearby Jupiter kept pulling them apart. Today, millions of asteroids probably inhabit the asteroid belt, with many more scattered throughout the solar system. Find out more from HubbleSite: Hubble discoveries about asteroids from NewsCenter . What is Planet X?

When astronomer Percival Lowell decided to search for a planet beyond Neptune in the 1930s, he called the object of his search "Planet X." This search led to the discovery of Pluto, but for many years some astronomers believed that another world larger than Pluto must exist undiscovered beyond Neptune. They thought this because Neptune's orbit seemed to be influenced by the gravity of an unseen planet. More recent studies indicate that Neptune's orbit is not influenced by undiscovered bodies, and that a large "Planet X" most likely does not exist. Some of the myths and misconceptions about Planet X are debunked on Phil Plait's Bad Astronomy website: The prospects for new planet discoveries in our solar system are small. However, astronomers are now finding hundreds of planets orbiting other stars. Has Hubble looked for Planet X? Astronomers are always on the lookout for new members of the solar system. The most active programs involve searches for new comets, asteroids and satellites of the outer planets, but a few scientists have undertaken an on-again, off-again search for planets beyond Neptune.

Astronomers can rule out an object as big as Jupiter orbiting a little further out than Neptune, since its gravitational effect on Neptuneï¿½s orbit would be pretty obvious. It would also be easily visible because of its brightness. To go undetected, a planet similar in size and composition to the other outer planets would have to be very far from the Sun. We do know of many other objects orbiting the Sun that are similar to Pluto, which belongs to the Kuiper Belt – a field of icy, comet-like bodies located beyond Neptune. In 2005, an object likely larger than Pluto, named Eris, was located in the Kuiper Belt. Find out more on HubbleSite: Dwarf Planets, Pluto, Kuiper Belt & Oort Cloud A diagram showing solar system orbits. The highly tilted orbit of Eris is in red. Dwarf Planets: 10 Need-to-Know Things Smaller Than Our Moon If the sun were as tall as a typical front door, Earth would be about the size of a nickel and dwarf planet Pluto, one of the larger known dwarf planets, would be the size of the head of a pin. Long Trip Dwarf planets orbit our sun, a star.

Most are located in the Kuiper Belt, a region of icy and rocky debris beyond Neptune. Ceres, the closest dwarf planet, is the largest world in the main asteroid belt between Mars and Jupiter. What's in a Day? Days on dwarf planets vary. One day on dwarf planet Ceres, for example, takes about nine Earth hours (the time it takes for Ceres to rotate once). It takes Ceres about 4.5 Earth years to go around the sun. Hard Worlds Dwarf planets are solid rocky and/or icy bodies. It all depends on their location in the solar system. Moon Check Dwarf planets cannot support life as we know it. World Class Pluto was considered a planet until 2006. But the discovery of similar worlds prompted scientists to change the definition of a planet to better describe the different kinds of worlds of our solar system. Dwarf Planets: Overview While similar to planets in many ways, dwarf planets share their orbits around the sun with other objects such as asteroids or comets.

The first five recognized dwarf planets are: Ceres | Pluto | Eris | Haumea | Makemake Dwarf Planets: In Depth Dwarf planets are a lot like regular planets: They both have enough mass and gravity to be nearly round - unlike odd-shaped asteroids. They both travel through space in a path around the sun. The big difference? A dwarf planet's path around the sun is full of other objects like asteroids and comets. A regular planet has a clear path around the sun. Most of the major impacts with other objects in its orbit happened billions of years ago. There is not much left over to get in the way. There may be dozens of dwarf planets in our solar system. So far, we've classified just a handful: Closest to home, Ceres is the largest and most unique resident of the main asteroid belt between Jupiter and Mars. It also is the first dwarf planet to be visited by a spacecraft - NASA's Dawn mission. Pluto is the most famous dwarf planet. Discovered in 1930, it was long classified as our solar system's ninth planet. Pluto and its busy system of moons orbits the sun in the Kuiper belt, a region of icy debris beyond Neptune.

Astronomers discovered Eris, a Pluto-sized world, in 2003. It takes icy Eris 557 Earth years to complete a single orbit around our sun. Two more confirmed orbit the sun in the icy zone beyond Neptune - Haumea and Makemake. Dwarf Planets: Trivia Little Rocks Dwarf planets are very different from their larger planetary cousins. It would take about 30,000 of them to create a world the size of Earth. Closest Dwarf Planet Ceres is the only dwarf planet found outside of the Kuiper Belt. Fast Football Dwarf planet Haumea is one of the fastest rotating objects in our solar system. Haumea spins so fast that it has pulled itself into the shape of a squashed American football. Bring a Flashlight High noon on Pluto would look a lot like a moonlit night here on Earth. The sunlight that reaches Pluto is about 1,000 times dimmer than what we see here on Earth and provides little warmth. Distance Runner Even though it traveled at speeds 30 times greater than the fastest fighter jet, NASA's New Horizons spacecraft still took more than nine years to get to Pluto.

Camera-Shy Planet Even our most powerful telescopes show little more than fuzzy blobs when pointed across billions of kilometers at Pluto and Charon. It took the New Horizons spacecraft nine and a half years of space travel to get the only close up images. Mission Milestone New Horizons is the only spacecraft to explore the Kuiper Belt up close. Long, Strange Trip Pluto is so far away it takes 248 years to orbit the sun -- so long it still hasn't finished one orbit since it was discovered in 1930. Pluto's orbit is so elliptical -- picture a squashed circle -- its distance from the sun varies more than 2.7 billion km (1.9 billion miles). New Class The discovery of Eris -- about the same size as Pluto -- far beyond Neptune sparked intense debate about the definition of a planet. In the end, Eris and Pluto were classified as dwarf planets. Deep Freeze Pluto is so cold even the air can freeze and fall to the ground like snow. The planet's average temperature is about -387 degrees Fahrenheit (-233 degrees Celsius). For comparison, the coldest spot on Earth gets down to -128 degrees Fahrenheit (-89 degrees Celsius).

Little Worlds, Big Numbers Scientists now consider that dwarf planets may be the most common type of planet. There are likely hundreds more dwarf planets out there waiting to be discovered. Faint Discovery There are millions of stars brighter than dwarf planet Pluto in the night sky, but observant astronomer Clyde Tombaugh caught a faint image -- light equal to a candle seen at a distance of 480 km (300 miles) -- on a photographic plate. Tombaugh had discovered the mysterious Pluto. Pluto Pluto nearly fills the frame in this image from the Long Range Reconnaissance Imager (LORRI) aboard NASA's New Horizons spacecraft, taken on July 13, 2015, when the spacecraft was 476,000 miles (768,000 kilometers) from the surface. Pluto: 10 Need-to-Know Things If the sun were as tall as a typical front door, Earth would be the size of a nickel and dwarf planet Pluto would be about the size of the head of a pin. Pluto orbits our sun, a star, at an average distance of 3.7 billion miles (5.9 billion kilometers) or 39.5 AU.

One day on Pluto takes about 153 hours. That's the time it takes for Pluto to rotate or spin once. Pluto makes a complete orbit around the sun (a year in Plutonian time) in about 248 Earth years. It is thought that Pluto has a rocky core surrounded by a mantle of water ice with other ices coating its surface. Pluto has five known moons. Pluto is sometimes called a double-planet system due to the fact that its moon Charon is quite large and orbits close to its parent planet. NASA's New Horizons spacecraft is the first mission sent to encounter the Pluto-system and other members of the Kuiper Belt. There are no known rings around Pluto. Pluto has a thin, tenuous atmosphere that expands when it comes closer to the sun and collapses as it moves farther away -- similar to a comet. Scientists do not think Pluto can support life as we know it. Although, some scientists believe it is possible Pluto could possess a hidden ocean under its surface. Pluto was considered a planet from 1930, when it was first discovered, until 2006.

The discovery of similar-sized worlds deeper in the distant Kuiper Belt sparked a debate which resulted in a new official definition of a planet. The new definition did not include Pluto. Pluto: Overview Discovered in 1930, Pluto was long considered our solar system's ninth planet. But after the discovery of similar intriguing worlds deeper in the distant Kuiper Belt, icy Pluto was reclassified as a dwarf planet. Findings by NASA's New Horizons in 2015 revealed for the first time how that Pluto is a complex and mysterious world. Information about Pluto and its largest moon, Charon, provide insight into the collision believed to have formed the dwarf planet and moons we see today. Dwarf planets may provide the best evidence about the origins of our solar system. Pluto: In Depth Pluto is classified as a dwarf planet and is also a member of a group of objects that orbit in a disc-like zone beyond the orbit of Neptune called the Kuiper Belt. This distant realm is populated with thousands of miniature icy worlds, which formed early in the history of our solar system. These icy, rocky bodies are called Kuiper Belt objects or transneptunian objects.

Pluto is about two-thirds the diameter of Earth's Moon and probably has a rocky core surrounded by a mantle of water ice. More exotic ices like methane and nitrogen frost coat its surface. Owing to its size and lower density, Pluto's mass is about one-sixth that of Earth's Moon. Pluto is more massive than Ceres - the dwarf planet that resides in the asteroid belt between Mars and Jupiter - by a factor of 20. Pluto's 248-year-long elliptical orbit can take it as far as 49.3 astronomical units (AU) from the Sun. (One AU is the mean distance between Earth and the Sun: about 150 million km or 93 million miles.) From 1979 to 1999, Pluto was actually closer to the Sun than Neptune, and in 1989, Pluto came to within 29.7 AU of the Sun, providing rare opportunities to study this small, cold, distant world. Since its orbit is so elliptical, when Pluto is close to the sun, its surface ices thaw, rise and temporarily form a thin atmosphere.

Pluto's low gravity (about 6 percent of Earth's) causes the atmosphere to be much more extended in altitude than our planet's atmosphere. Pluto becomes much colder during the part of each orbit when it is traveling far away from the sun. During this time, the bulk of the planet's atmosphere is thought to freeze. Pluto has a very large moon that is almost half its size named Charon, which was discovered in 1978. This moon is so big that Pluto and Charon are sometimes referred to as a double dwarf planet system. The distance between them is 19,640 km (12,200 miles). The Hubble Space Telescope photographed Pluto and Charon in 1994 when Pluto was about 30 AU from Earth. These photos showed that Charon is grayer than Pluto (which appears to have a slightly red hue), indicating that they have different surface compositions and structures. Charon's orbit around Pluto takes 6.4 Earth days, and one Pluto rotation (a Pluto day) takes 6.4 Earth days.

Charon neither rises nor sets, but hovers over the same spot on Pluto's surface, and the same side of Charon always faces Pluto -- this is called tidal locking. Compared with most of the planets and moons, the Pluto-Charon system is tipped on its side, like Uranus. Pluto's rotation is retrograde: it rotates backwards, from east to west (Uranus and Venus also have retrograde rotations). It isn't known whether Pluto has a magnetic field, but its small size and slow rotation suggest little or no magnetic field. Because Pluto and Charon are so small and far away, they are extremely difficult to observe from Earth. In the late 1980s, Pluto and Charon passed in front of each other repeatedly for several years. Observations of these rare events allowed astronomers to make rudimentary maps of each body showing areas of relative brightness and darkness. In 2005, scientists photographing Pluto with the Hubble Space Telescope in preparation for the New Horizons mission found two tiny moons orbiting in the same plane as Charon. These two moons, named Nix and Hydra, are two to three times farther away from Pluto than Charon.

In 2011 and 2012, scientists used Hubble to spot two more moons (originally designated P4 and P5). In 2013, the two moons were named Kerberos (P4) and Styx (P5). Late in 2014 and early in 2015, image animations displayed the mutual orbital waltz of Pluto and Charon around their center of mass. Beginning in the spring of 2015, New Horizons started its detailed studies of Pluto including searches for additional moons and for rings. Various studies continued through its close approach on July 14 at a distance of 8507 miles (13,691 kilometers) and after. The return of New Horizons' best data began shortly after its close approach and will continue for more than a year due to the large transmission distance. Because of the speed of the flyby and Pluto's slow rotation rate only one hemisphere of this dwarf planet has been photographed and measured at high resolution, limiting generalizations about all of Pluto's surface.

Still, Pluto's diameter could be measured and had to be revised upward to 1475 miles (2,374 kilometers) based on New Horizons' imagery. Results from New Horizons, besides forcing the revision of textbooks, left planetary scientists struggling to explain this cold, distant world and its system of moons. Pluto's surface exhibits craters as large as 162 miles (260 kilometers) in diameter on the dayside, near encounter hemisphere. Craters are widely distributed there and show degradation or infill. This was a surprise to find on a dwarf planet that was anticipated to be heavily cratered and lacking activity that might affect craters. Dense cratering is seen in some areas, but so are tectonic features including scarps and troughs as long as about 370 miles (600 kilometers). Mountains are also seen rising 6500 to 9800 feet (2 to 3 kilometers) above their surroundings. The likely materials that can hold up the mountains and maintain their shapes over millions of years in Pluto's cold is limited.

The science team concludes that the mountains are made of "water ice-based 'bedrock'." Frozen gases on Pluto's surface (the temperature there is about -391 F = -235 C = 38 K) include nitrogen (N2), carbon monoxide (CO),and methane (CH4). These were detected by ground-based telescopes and are now thought to be thin layers on top of the 'bedrock' water ice. Dark surface coloring appears to be due carbon residues called tholins. These are created by solar ultraviolet rays or charged particles falling on mixtures of nitrogen and methane. Detailed views of a plain on this dwarf planet show no confirmed craters but it has large (tens of kilometers) polygonal or egg-shaped features defined and separated by troughs between neighbors. Features similar in look to glaciers on Earth are seen in this region. This is consistent with the strength and flow properties of the frozen gases mentioned above. Radio transmission measurements from New Horizons measured Pluto's atmosphere having a pressure of 10 microbars (millionths of a bar). For comparison, Earth's atmospheric pressure at sea level is about 1 bar, 100,000 times greater than Pluto's surface pressure.

Those measurements also showed that Pluto has a shallow tropospheric boundary layer (Earth has a troposphere too). Imagery from the cameras shows a haze layer and even some structure in it. It isn't known whether Pluto has a magnetic field, but its small size and slow rotation suggest little or none. Data from two of New Horizons instruments may give an indirect answer to this question. Charon was also studied in detail. Its diameter came out slightly larger than expected, at 753 miles (1212 kilometers). Surface variations of 9800 feet (3 kilometers) seen on this moon imply that it, like Pluto, has water ice that runs deep in its structure. Also similar to Pluto, Charon exhibits cratered and smooth plains, fault scarps, and an extensive system of faults and graben. (A graben [Grah-ben] is a block of surface material that has dropped lower than its surroundings, creating a wide valley whose walls are the fault planes along which the block dropped.) Rolling plains are moderately cratered. They even show several rille-like structures (first observed on Earth's moon).

Craters with rays (both light, as on Earth's moon, and dark, as sometimes seen on Mars) indicating freshness are found on Charon. Other craters show evidence of aging. The two largest fractures (visible during the flyby) on Charon extend at least 650 miles (1050 kilometers) across the surface and at least one other, with a depth of 3 miles (5 kilometers) is seen going over the horizon to Charon's night side. One of the dayside fractures is seen as a double-walled graben-like structure. There is no evidence that Charon has an atmosphere. Nix is not spherical. It has three different diameters (making it a tri-axial ellipsoid): 67 x 51 x 45 miles (108 x 82 x 72 kilometers). There are variations in composition over its surface but it reflects more light than Charon. This suggests that its ice is cleaner than Charon's. Hydra is also not spherical with rough diameters of 53 x 41 miles (86 x 66 kilometers) with the third dimension not well determined.

It also is more reflective than Charon, leaving scientists to puzzle over how the ice on these small moons could stay so bright over billions of years given the processes known to darken material over time. More information on Kerberos and Styx awaits the return of more data from New Horizons. Data used for searches for additional moons and rings has not detected any. How Pluto Got its Name Pluto is the only world named by an 11-year-old girl. In 1930, Venetia Burney of Oxford, England, suggested to her grandfather that the new discovery be named for the Roman god the underworld. He forwarded the name to the Lowell Observatory and it was selected. Pluto's moons are named for other mythological figures associated with the underworld. Charon is named for the river Styx boatman who ferries souls in the underworld; Nix is named for the mother of Charon, who is also the goddess of darkness and night; Hydra is named for the nine-headed serpent that guards the underworld; Kerberos is named after the three-headed dog of Greek mythology; and Styx is named for the mythological river that separates the world of the living from the realm of the dead.

Pluto's place in mythology can get a little muddled, so we asked Dr. Elizabeth Vandiver, chair of the Department of Classics in Whitman College in Walla Walla, Washington, to clarify the origins of the name: "Pluto is the name of the Roman god of the Underworld, equivalent to the Greek Hades. However, the Greek name "Plouton" (from which the Romans derived their name "Pluto") was also occasionally used as an alternative name for Hades. But Pluto is definitely the Roman spelling." The symbol for dwarf planet Pluto is a monogram made up of P and L in Pluto (and also the initials of Percival Lowell, who predicted its discovery). Pluto: Significant Dates 1930: Clyde Tombaugh discovers Pluto. 1977-1999: Pluto's lopsided orbit brings it slightly closer to the sun than Neptune. It will be at least 230 years before Pluto moves inward of Neptune's orbit for 20 years. 1978: American astronomers James Christy and Robert Harrington discover Pluto's unusually large moon, Charon. 1988: Astronomers discover that Pluto has an atmosphere.

2005: Scientists using the Hubble Space Telescope announce the discovery of two additional moons of Pluto. Named Nix and Hydra, the little moons may have formed at the same time as Charon did, perhaps all three splitting off from Pluto in a giant impact event. 2006: NASA's New Horizons mission launches on a path to explore Pluto and the Kuiper Belt region. The spacecraft is scheduled to reach Pluto in 2015. 2006: The International Astronomical Union classifies Pluto as a dwarf planet and recognizes similar worlds beyond the orbit of Neptune as plutoids. 2011: Astronomers using the Hubble Space Telescope discovered a fourth moon, named Kerberos, orbiting the icy dwarf planet. 2012: Astronomers using the Hubble Space Telescope to search for potential hazards to the New Horizon mission discovered a fifth moon, named Styx, orbiting the icy dwarf planet. Pluto: Trivia Pluto's estimated surface temperature falls between --378 to --396 degrees F (-228 to -238 C). Planet Hunter Pluto was discovered in 1930 by American astronomer Clyde Tombaugh.

Big Companion Charon is half of Pluto's diameter - making it the largest satellite relative to the planet it orbits. Long Year Pluto orbits the Sun once every 248 years. That's longer than the entire history of the United States of America. Slow Communication A radio signal moving at the speed of light takes about 4 hours to reach Pluto from Earth. Shifting Scene Pluto's brightness changes as it rotates, revealing large light and dark regions. Dark Mythology Pluto is named after the Roman god of the underworld. How Pluto Got Its Name Student Venetia Burney suggested the name Pluto in 1930. Scary Boat Charon is named after the mythological boatman who ferried souls across the river Styx to Pluto for judgment. Tribute The symbol for Pluto ("PL") is tribute to Percival Lowell, who started the search for the ninth planet in the early 1900s. Small World At 1,470 miles (about 2,370 kilometers) across, Pluto could fit between Washington, D.C. and Denver, Colorado. Sideways Like Uranus, Pluto rotates on its side.

Far From the Sun Pluto's last time at aphelion - the farthest point in its orbit - was 1865. It will next reach aphelion in 2112. Lightweight A person on Pluto would weigh 1/15 what they weigh on Earth . The astronauts on the Moon had 1/6 of their Earth weight. Close Companion Charon is 20 times closer to Pluto than our moon is to Earth. Moon Surprise American astronomers James Christy and Robert Harrington discovered Charon in 1978. Kuiper Belt Artist's concept of Eris and its moon. The sun is in the distance. Image credit: Robert Hurt (IPAC). Kuiper Belt: 10 Need-To-Know Things The Kuiper Belt and the Oort Cloud are regions of space. The known icy worlds and comets in both regions are much smaller than Earth's moon. The Kuiper Belt and the Oort Cloud surround our sun, a star. The Kuiper Belt is a doughnut-shaped ring, extending just beyond the orbit of Neptune from about 30 to 55 AU.

The Oort Cloud is a spherical shell, occupying space at a distance between five thousand and 100 thousand AU. Long-period comets (which take more than 200 years to orbit the sun) come from the Oort Cloud. Short-period comets (which take less than 200 years to orbit the Sun) originate in the Kuiper Belt. There may be are hundreds of thousands of icy bodies larger than 100 km (62 miles) and an estimated trillion or more comets within the Kuiper Belt. The Oort Cloud may contain more than a trillion icy bodies. Some dwarf planets within the Kuiper Belt have thin atmospheres that collapse when their orbit carries them farthest from the sun. The Kuiper Belt and the Oort Cloud are regions of space and therefore do not have moons. However, several dwarf planets within the Kuiper Belt have moons. The Kuiper Belt and the Oort Cloud are regions of space and therefore do not have rings. No objects within these two regions are known to have rings. The first mission to the Kuiper Belt is New Horizons. New Horizons will reach Pluto in 2015.

These two regions of space are not capable of supporting life as we know it. Fact: Both the Kuiper Belt and the Oort Cloud are named for the astronomers who predicted their existence during the 1950s: Gerard Kuiper and Jan Oort. Kuiper Belt: In Depth The Kuiper Belt is a disc-shaped region beyond Neptune that extends from about 30 to 55 astronomical units (compared to Earth which is one astronomical unit, or AU, from the sun). This distant region is probably populated with hundreds of thousands of icy bodies larger than 100 km (62 miles) across and an estimated trillion or more comets. Dwarf planet Pluto may be the best known of the larger objects in the Kuiper Belt. Comets from the Kuiper Belt take less than 200 years to orbit the sun and travel approximately in the plane in which most of the planets orbit the sun. .Objects in the Kuiper Belt are presumed to be remnants from the formation of the solar system about 4.6 billion years ago.

The first of these strange bodies, which astronomers call Kuiper Belt Objects (KBOs), came to light in 1992, discovered by Dave Jewitt and Jane Luu -- a pair of scientists who didn't believe the outer solar system was empty. Beginning in 1987 they had doggedly scanned the heavens in search of dim objects beyond Neptune. It took five years, looking off-and-on through the University of Hawaii's 2.2 m telescope, but they finally found what they were after: a reddish-colored speck 44 AU from the Sun -- even more distant than Pluto! Jewitt (University of Hawaii) and Luu (UC Berkeley) wanted to name their find "Smiley," but it has since been cataloged as "1992 QB1." That discovery marked our first glimpse of the long-sought Kuiper Belt, named after Gerard Kuiper who, in 1951, proposed that a belt of icy bodies might lay beyond Neptune. It was the only way, he figured, to solve a baffling mystery about comets: Some comets loop through the solar system on periodic orbits of a half-dozen years or so.

They encounter the Sun so often that they quickly evaporate -- vanishing in only a few hundred thousand years. Astronomers call them "short-period comets," although "short-lived" is more to the point. Short-period comets evaporate so quickly compared to the age of the solar system that we shouldn't see any, yet astronomers routinely track dozens of them. It was a real puzzle. Kuiper's solution was a population of dark comets circling the Sun in the realm of Pluto -- leftovers from the dawn of our solar system when planetesimals were coalescing to make planets. The ones beyond Neptune, Kuiper speculated, never stuck together, remaining instead primitive and individual. Nowadays they occasionally fall toward the Sun and become short-period comets. Because KBOs are so distant, their sizes are difficult to measure. The calculated diameter of a KBO depends on assumptions about how reflective the object's surface is. With infrared observations by the Spitzer Space Telescope, most of the largest KBOs have known sizes. One of the most unusual KBOs is Haumea, which is a part of a collisional family orbiting the sun.

The parent body, Haumea, apparently collided with another object that was roughly half its size. The impact blasted large icy chunks away and sent Haumea reeling, causing it to spin end-over-end every four hours. It spins so fast that it has pulled itself into the shape of a squashed American football. Haumea and two small moons -- Hi'iaka and Namaka -- make up the family. In March 2004, a team of astronomers announced the discovery of a planet-like transneptunian object orbiting the sun at an extreme distance, in one of the coldest known regions of our solar system. The object (2003VB12), since named Sedna for an Inuit goddess who lives at the bottom of the frigid Arctic ocean, approaches the sun only briefly during its 10,500-year solar orbit. It never enters the Kuiper Belt, whose outer boundary region lies at about 55 AU -- instead, Sedna travels in a long, elliptical orbit between 76 and nearly 1,000 AU from the sun.

Since Sedna's orbit takes it to such an extreme distance, its discoverers have suggested that it is the first observed body belonging to the inner Oort Cloud. In July 2005, a team of scientists announced the discovery of a KBO that was initially thought to be about 10 percent larger than Pluto. The object, temporarily designated 2003UB313 and later named Eris, orbits the sun about once every 560 years, its distance varying from about 38 to 98 AU. (For comparison, Pluto travels from 29 to 49 AU in its solar orbit.) Eris has a small moon named Dysnomia. More recent measurements show it to be slightly smaller than Pluto. The discovery of Eris -- orbiting the sun and similar in size to Pluto (which was then designated the ninth planet) -- forced astronomers to consider whether Eris should be classified as the tenth planet. Instead, in 2006, the International Astronomical Union created a new class of objects called dwarf planets, and placed Pluto, Eris and the asteroid Ceres in this category.

In 2015, NASA's New Horizons spacecraft flew past Pluto, making the first up-close exploration of a Kuiper Belt Object. The spacecraft is continuing deeper into this region of icy debris and may be able to explore at least one more object. How the Kuiper Belt Got Its Names The region is named for the astronomer who predicted its existence -- Gerard Kuiper. It is sometimes called the Edgeworth-Kuiper Belt, recognizing the independent and earlier discussion by Kenneth Edgeworth. Objects discovered in the Kuiper Belt get their names from diverse mythologies. Eris is named for the Greek goddess of discord and strife. Haumea is named for a Hawaiian goddess of fertility and childbirth. Comets from both regions are generally named for the person who discovered them. Significant Dates 1943: Astronomer Kenneth Edgeworth suggests that a reservoir of comets and larger bodies resides beyond the planets. 1950: Astronomer Jan Oort theorizes that a vast population of comets may exist in a huge cloud on the distant edges of our solar system. 1951: Astronomer Gerard Kuiper predicts the existence of a belt of icy objects just beyond the orbit of Neptune.

1992: After five years of searching, astronomers David Jewitt and Jane Luu discover the first KBO, 1992QB1. 2002: Scientists using the 48-inch Oschin telescope at Palomar Observatory find Quaoar, the first large KBO hundreds of kilometers in diameter. This object was photographed in 1980, but was not noticed in those images. 2004: Astronomers using the 48-inch Oschin telescope announce the discovery of Sedna (2003VB12). 2005: Astronomers announce the discovery of 2003UB313. This object, later named Eris, is slightly larger than Pluto. 2008: The Kuiper Belt object provisionally known as 2005FY9 ("Easterbunny") is recognized in July as a dwarf planet and named Makemake (pronounced MAHkeh-MAHkeh) after the Polynesian (Rapa Nui) creation god. In September, 2003EL61 ("Santa") was designated a dwarf planet and given the name Haumea after the Hawaiian goddess of fertility and childbirth.

This 2013 graphic puts huge solar system distances in perspective. Oort Cloud: 10 Need-To-Know Things The Oort Cloud is a region of space. The known comets in this region are much smaller than the Earth's moon. The Oort Cloud surrounds our sun, a star. The Oort Cloud is a spherical shell, occupying space at a distance between five and 100 thousand AU. Long-period comets (which take more than 200 years to orbit the sun) come from the Oort Cloud. The Oort Cloud may contain more than a trillion icy bodies. Comets that originate from the Oort Cloud gain atmospheres (the coma) when they near the sun. This atmosphere collapses when the comet's orbit carries it farthest from the sun. There are no known moons of Oort Cloud objects. The are no known rings around objects in this region of space. There have been no missions sent to the Oort Cloud. The Oort Cloud is not capable of supporting life as we know it. The Oort Cloud is named for the astronomer who predicted its existence during the 1950s: Jan Oort.

Oort Cloud: In Depth The Oort Cloud is believed to be a thick bubble of icy debris that surrounds our solar system. This distant cloud may extend a third of the way from our sun to the next start -- between 5,000 and 100,000 astronomical units. Earth is about one astronomical unit from the sun (roughly 93 million miles or 150 million kilometers). Consider this: At its current speed of about a million miles a day, NASA's Voyager 1 spacecraft won't reach the Oort Cloud for about 300 years. And it will take about 30,000 years to reach the other side. Dutch astronomer Jan Oort first proposed the idea of this region of space to explain the origins of comets with that take thousands of years to orbit the sun. These are called long-period comets and most have been seen only once in recorded history. More frequent visitors to the inner solar system are called short-period comets. There may be hundreds of billions, even trillions, of icy bodies in the Oort Cloud. Every now and then, something disturbs one of these icy worlds and it begins a long fall toward our sun.

Two recent examples are comets C/2012 S1 (ISON) and C/2013 A1 Siding Spring. ISON was destroyed when it passed too close the the sun. Siding Spring, which made a very close pass by Mars, will not return to the inner solar system for about 740,000 years. How the Oort Cloud Got its Name This region of space is named for Dutch astronomer Jan Oort who predicted its existence in 1950. Discovery The Oort Cloud still hasn't been discovered. It is just a theory, although we have studied several comets believed to have come from this distant region of our galaxy. The Solar System The Solar System Our Solar System is an amazing place. Not only is it home to eight planets, it also hold several dwarf planets, hundreds of moons, and thousands of stars and asteroids. The eight planets in our Solar System are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. These planets orbit the Sun. Here is a funny song to help you remember the planets The Sun The Sun is the center of our Solar System. It is because of the Sun that our solar system gets its name.

Sol is the Roman name for Sun. The Sun is the largest object within the Solar System - it makes up more than 95% of all the matter! It is because of the Sun's large size that the rest of the objects within the Solar System orbit around it. The Sun is very, very hot. It is 10,000 degrees Fahrenheit on its surface. Mercury Mercury is the closest planet to the Sun, making it the first planet in the Solar System. It is named after the Roman messenger god. In mythology, the god was known for being quick - Mercury is the fastest of all the planets to orbit the Sun, because it has the smallest route it has to take! Mercury can occasionally be seen from Earth Mercury is the second densest planet in the Solar System It is mainly made up of iron There is no atmosphere on Mercury Despite its fast trip around the Sun, Mercury's revolution is very slow - one day on Mercury equals about 59 days on Earth! Venus Venus is the second planet from the Sun. It is named after the Roman goddess of beauty and love. Venus is almost the same size as Earth, but other than size the two planets are very different!

Fun Facts about Venus Venus appears to be the brightest planet in the sky due to the reflection of the Sun from its clouds, and its closeness to Earth Venus has an incredibly thick atmosphere. This makes it the hottest of the inner planets Venus rotates East to West Venus is covered in volcanoes Venus does not have any moons Earth Earth is the only known planet that has any life forms in the Solar System. It is the third planet from the Sun. It is the only planet that is not named after a god. Most of the Earth is covered in water - 70%! Earth has a thin atmosphere, that protects us from dangerous gasses and heat in space Earth is the largest of the inner planets Air, water, and land make up the Earth Earth's axis is tilted at 23.5 degrees This a video showing the many different life forms that Earth has Mars Mars is the fourth planet from the Sun. Named for the Roman god of war, it is also known as the "Red Planet". It is the last of the inner planets.

Temperatures on Mars are very similar to temperatures on Earth It is believed that Mars once had water on its surface Mars is called the red planet because its surface is covered in red dust The largest volcano in the Solar System is on Mars. It is called Olympus Mons Mars has two small moons Jupiter Jupiter is the first of the outer planets, and the fifth planet from the Sun. It is named for the king of the Roman gods. It is the largest of all of the planets. Fun Facts about Jupiter Jupiter is best known for its "Great Red Spot" - a mass of hurricanes that have been storming for hundreds of years. The spot is larger in size than that of Earth Jupiter is made up of gasses - there is no solid surface on it Jupiter is so big; Earth could fit inside of it more than 1,000 times! Jupiter has over 50 moons. Four of these moons are as big as planets Jupiter has the most active volcanic activity in the Solar System Learn more about the Great Red Spot! Saturn Saturn is the sixth planet from the Sun. It is named for the Roman god of agriculture. It is most well known for its highly visible rings.

Other Features of the Solar System There are many other exciting elements in the Solar System. Here are a few. Asteroids Asteroids are rocky bodies in the Solar System that are too small to be considered actual planets. In between Mars and Jupiter lies the Asteroid Belt, containing well over 90,000 asteroids. Comets Comets are ice and rock that grow tails the closer they get to the sun. The hotter they get, the longer this "tail" becomes. The sunlight makes comets glow, which causes them to be visible on Earth. Dwarf Planets Dwarf planets are bodies that orbit the sun that are not considered large enough to be actual planets. The most famous dwarf planet is Pluto, which was considered an actual planet up until 2006. Satellites Satellites are machines put into the Solar System by scientists in order to find out more about the Solar System, and what is in it. These machines take pictures, perform experiments, take data, and much, much more. Without them, we wouldn't have the vast amount of information that we have today. Summary The Solar System is a fascinating place. Each of the eight planets have their own unique features, but are also similar in some ways - much like people!

It is amazing to think that the Solar System has been around for more than 4.6 billions years. Each of the eight planets orbits the sun in the same direction, and in their own time. We have so much more we can learn about the Solar System, and so much we have learned already today. sit this page to learn more interesting facts about the Solar System! Want to get an idea of how far apart the planets are? Click here! Resources Our Solar System. Retrieved from Solar System. Retrieved from Facts about Celestial Bodies in Our Solar System Learning About Our Solar System written by: Jason C. Chavis•edited by: George Adcock •updated: 1/10/2011 The celestial bodies in our Solar System are divided into different sections: the inner planets of Mercury, Venus, Earth and Mars separated by the asteroid belt from the outer planets of Jupiter, Saturn, Uranus and Neptune. Each celestial body is made of a different type of material: rock, gas or ice. slide 1 of 4 The celestial bodies in our Solar System are divided into two regions, based on the structure and size of the planets.

The first region of the Solar System is commonly referred to as the inner planetary area, containing the first four planets, which are rocky worlds. This is set apart from the outer planets by the asteroid belt . The outer planets are the four gas giants. Surrounding the entire system is the Kuiper belt , a collection of icy bodies beyond Neptune. Above right: Planets. (Supplied by NASA; Public Domain; slide 2 of 4 Types of Celestial Bodies According to the accepted modern theory, the objects in the Solar System are segmented into three distinct classifications: planets, dwarf planets and other small bodies. Each of these are defined by the International Astronomical Union. In order for a body to be classified as a planet, it must maintain three specific criteria. First, it must be in orbit around the Sun. Second, it must contain enough mass to have formed into a spherical shape. A planet must also have cleared its orbital neighborhood of all other objects, with the exception of moons and orbital rings. By this definition, the Solar System only possesses eight known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

When Pluto was redacted from the planetary list due to its small size and highly eccentric orbit , it created an uproar within the scientific community. Now designated a dwarf planet or plutoid, Pluto is joined by other objects that fit the criteria of maintaining orbit around the Sun and being large enough to be spherical. The major ones include Ceres, Haumea, Makemake, Eris, Sedna, Orcus and Quaoar. Even so, the California Institute of Technology estimates there are thousands more. Any other object in orbit around the Sun is simply a small celestial body. These include asteroids, meteors and satellites. slide 3 of 4 Composition of Celestial Bodies Celestial bodies in our Solar System are composed of three classes of material: ice, gas and rock. The inner part of the Solar System is principally rock material, usually remaining solid no matter the environmental conditions caused by the Sun. Still, there are limited instances of both ice and gas within this region. The giant planets of the outer solar system are mostly gas, made primarily of hydrogen, helium and neon. Jupiter and Saturn are the most extensive examples of gas bodies. The outer edge of the Solar System is mostly composed of ice.

Uranus and Neptune are generally considered ice planets, although there is believed to be occasional gas activity. The Kuiper belt is believed to be pretty much completely ice. There are numerous features for the celestial bodies in our Solar System which define the way we look at their structure and formation. According to astronomers and space scientists, it is likely that any other planetary system capable of supporting life will have a relatively similar structure. This gives us a platform for which to standardize our search for life outside our planet. slide 4 of 4 "Solar System Exploration" NASA: Extreme Science:

Question: What is the name of the thousands of small bodies which orbit the Sun?
Answer: Asteroids